Many known hearing devices must be adapted or fitted to the particular individual who is to be using the hearing device, i.e. the user. Such fitting may be necessary in order to account for e.g. differing hearing capabilities and/or differing anatomic features of the ear, and typically comprises setting a maximum gain for the hearing device in order to prevent feedback-generated oscillations during use of the hearing device. Fitting is typically performed by a hearing-care professional (HCP or “dispenser”) by means of a fitting apparatus connected to the hearing device.
Patent application EP 1 708 544 discloses a system and a method for measuring vent effects in a hearing aid. During a self-test performed at the beginning of a fitting session, the hearing aid generates an electric tone signal in an electric signal path between the hearing-aid microphone and the hearing-aid loudspeaker, picks up the acoustic feedback from the loudspeaker to the microphone, and generates a correlation signal based on a comparison between the electric tone signal and the acoustic feedback. The hearing aid then calculates acoustic properties of the vent based on the correlation signal. If the calculated acoustic properties deviate from previously stored properties, the HCP is informed and may then e.g. modify the length or the diameter of the vent or lower the gain of the hearing aid.
Patent EP 1 310 138 B1 discloses a hearing aid in which the signal path between the microphone and the loudspeaker is blocked during a comfort delay period after start-up of the hearing aid in order to avoid feedback-generated oscillations during insertion of the hearing aid into the ear. During the comfort delay period, the hearing aid generates an acoustic signal in order to notify the user that the hearing aid is switched on and is operative.